In recent years, power carrier communication has attracted attention as a communication system capable of constituting a local area network (LAN) without performing an additional wiring work in a home network. In the power carrier communication, security is ensured by encrypting communication data using an encryption key shared by a base unit and a slave unit. In the power carrier communication, an authentication process for sharing the encryption key is performed. For the method of the authentication process, for example, there is a technique in which an authentication process between a base unit and a slave unit is carried out in the situation where buttons provided in the base unit and the slave unit are pushed down within a predetermined time (see Patent Literature 1).